“like shooting fish in a barrel”别理解成“像在桶里抓鱼”，引申为很容易办到的事，没有挑战的事，瓮中捉鳖。

【例句】
What do you mean you can't do it? It'll be like shooting fish in a barrel!
你说干不了是什么意思？这是很容易办到的事！

Jane's a good mechanic . Changing a tire is like shooting fish in a barrel , for her.
简是个好技工。对她来说，换轮胎这样的事简直是易如反掌。